Authentication method, notification method, source device, and sink device

A method for use in a source device includes: acquiring a random number; transmitting the random number to a sink device through a High Definition Multimedia Interface-Consumer Electronics Control (HDMI-CEC) bus; receiving first signature information and capability information from the sink device through the HDMI-CEC bus, the first signature information being information in which the random number is encrypted with a first secret key of the sink device, the capability information being information about a display capability of the sink device; acquiring a result of a first determination whether first decrypted information is compatible with the transmitted random number, the first decrypted information being obtained by decrypting the first signature information with a first public key paired with the first secret key; determining that the received capability information is correct information when the result of the first determination is that the first decrypted information is compatible with the transmitted random number; and outputting video corresponding to the capability information to sink device.